Dither-tuned tunable microwave tube apparatus



April 29, 1969 I of 2 Sheet Filed June 15, 1966 771 m w R G W 2 w I w m N U T MAGNET CATHO DE INSU LATOR FIG. 3

INVENTOR.

' FIG. I

FIG. 4

' HERBERT H. CHUN M 11 1 ATTORNEY.

7 April 29, 1969 H. H. CHUN 3,441,794 DITHER-TUNED TUNABLE MICROWAVE TUBE APPARATUS Filed June 15, 1966 Sheet 2' of 2 FIG. 2

INVENTOR.

HE BERT H. CHUN BY 7 v Lgb jnvdk 9 ATTORNEY United States Patent M US. Cl. 315-39.61 8 Claims ABSTRACT OF THE DISCLOSURE A dither-tuned microwave tube is disclosed. The tube includes a tuning mechanism for tuning the operating frequency to a certain center frequency within a certain relatively broadband of frequencies. A motor is coupled to the tuning mechanism through the intermediary of an eccentric cam on a crank shaft for oscillating the tuning structure at a relatively high frequency to dither the operating frequency over a narrow band of frequencies centered at the first certain frequency. The tuner structure includes an elongated actuating member coupled at one end to the motor and coupled at the other end to the tuning structure operating within the microwave circuit. Intermediate the length of the tuner actuating member includes a nut forming a first portion and a threaded rod mating with the nut forming the second portion and means for producing rotation of one of the members relative to the other, whereby the length of the activating mechanism is changed to change the frequency about which the tube is dithered.

Heretofore, dither-tuned microwave magnetron power output tubes for radars have been built. Such a magnetron is described and claimed in copending US. application 487,697 filed Sept. 16, 1965 now issued as US. Patent 3,414,761 on Dec. 3, 1968 and assigned to S-F-D Laboratories, Inc., a subsidiary of the assignee of the present invention. In this tube a tuning plunger is movable within a cavity coupled to the vane resonator system for tuning the frequency of the cavity and thus the operating frequency of the vane resonator system. An elongated flexible actuating rod was coupled to the tuning plunger at one end and extended out of the tube to a ball bearing assembly coupled to a transverse eccentric rotating shaft. The eccentric shaft was driven by a motor at a high speed as of 12,000 rpm. to cause the tuning plunger and rod to oscillate axially for a distance of about plus and minus 0.0015 about some mean axial position of the tuning plunger. The plunger actuating rod had a fixed length and the position of the transverse eccentric shaft was fixed such that the tube was dither-tuned only about some predetermined fixed frequency. The plunger actuating rod was made flexible to accommodate the side whipping of the rod due to the eccentricity of the rotating driving shaft. The problem with this prior arrangement was that it did not have provisions for changing the mean position of the plunger and actuating rod such that all such tubes had a fixed predetermined operating frequency about which they were dither-tuned.

In the present invention, the tube is tunable to various selectable first frequencies within a band of frequencies about which selected first frequency the tube is dithered or frequency modulated over a narrow band of frequencies. This is accomplished, in the apparatus of the present invention, by varying the length of the tuning plunger actuating rod for selecting the first frequency about which the tube is dither-tuned by oscillating the rod and plunger. In a preferred embodiment of the present invention, the tuner actuating rod is varied in length by making a portion of the actuating rod out of a rotatable nut threadably 3,441,794 Patented Apr. 29, 1969 mating with the threaded end of a second portion of the rod which is connected to the tuning plunger and which is prevented from turning with the rotatable nut. Thus rotation of the nut causes the composite actuating rod assembly to vary in length for tuning of the tube to the various frequencies about which the tube is dithered. In the preferred embodiment, the nut portion of the composite actuating rod is connected to the eccentric shaft through the intermediary of a ball and socket joint, whereby the side to side whipping action of the outer end of the composite actuating rod as well as rotation of the nut is accommodated. The nut is turned from an axially stationary rotatable gear through the intermediary of an axially flexible spider and/ or spline type bearing.

The principal object of the present invention is the provision of a tunable dithered microwave tube apparatus.

One feature of the present invention is the provision of a dithered tuning rod which is axially variable in length for selecting the frequency of the tube about which its output frequency is dithered (frequency modulated).

Another feature of the present invention is the same as the preceding feature wherein the tuning rod is made axially variable in length by making a portion of the rod out of a rotatable nut which threadably mates with a threaded second portion of the rod.

Another feature of the present invention is the same as the preceding feature wherein the nut portion of the composite rod is driven from an eccentric shaft through the intermediary of a yoke like bearing assembly connected to the rod by a ball and socket joint to accommodate rotation of the nut and side to side whipping of the yoke coupling to the eccentric shaft.

Another feature of the present invention is the same as the preceding feature wherein the nut is rotated from an axially stationary gear by means of a flexible spider and/ or a spline or key type coupling.

Other features of the present invention will become apparent upon a perusal of the following specification taken in connection with the accompanying drawings wherein:

FIG. 1 is an elevational view of a magnetron tube incorporating the features of the present invention,

FIG. 2 is an enlarged longitudinal sectional view of the magnetron of FIG. 1 taken along line 22 in the direction of the arrows,

FIG. 3 is a sectional view of the structure of FIG. 2 taken along line 3-3 in the direction of the arrows, and

FIG. 4 is a sectional view of the structure of FIG. 2 taken along line 4-4 in the direction of the arrows.

Referring now to FIG. 1 there is shown a magnetron microwave tube 1 employing features of the present invention. The microwave tube is of the conventional coaxial type and includes a cylindrical tube body 2 with a cathode insulator assembly 3 coaxially depending from the main body 2. A double C-shaped magnet assembly '4 is affixed to pole pieces on opposite axial ends of the tube body 2 to provide an axially directed magnetic field in the interaction region of the magnetron internally of the main body portion 2. A tuner housing assembly 5 is mounted on the top of the main body 2 and contains the tuner actuating mechanism therein for tuning the magnetr-on 1 over its tunable frequency band such as, for example, from 16 to 17 gHz. A tuner drive mot-or 6 is disposed at the top of the tuner housing 5 for dither-tuning (frequency modulating) the output frequency of the magnetron about some selected frequency with-in the tunable band of the magnetron 1. A resolver 7 is affixed to the output shaft of the motor to produce an output signal representative of the instantaneous frequency deviation of the magnetron output signal from its preselected frequency, i.e., carrier frequency. The output microwave signal is extracted from the tube 1 via output waveguide 8.

Referring now to FIG. 2 the tuner apparatus is shown in greater detail. The microwave portion of the magnetron tube 1 includes an axially disposed cathode emitter 9. An array of inwardly directed vane resonators 11 are disposed surrounding the cathode emitter 9 to define an annular magnetron interaction region 12 in the space therebetween in which the fields of the vane resonators interact with a stream of electrons circulating around the emitter 9. An axially directed magnetic field passes axially through the interaction region 12 from one magnetic pole piece 13 to an axially opposed pole piece 1'4. A cylindrical anode wall 15 surrounds the vane array 11 supporting the vanes from their root portions. A circular electric mode cavity resonator 16 surrounds the anode wall 15 and communicates with the vane array via an array of axially directed coupling slots 17 cut through the wall 15 into the back portion of every other vane resonator. The coaxial cavity 16 serves to lock the frequency of the o mode of the vane resonator system to the excited TE mode of the cavity 16.

The coaxial cavity and thus the vane system is tuned by means of a tuning plunger 18 axially movable of the cavity 16. Thus axial movement of the plunger 18 tunes the output frequency of the microwave output signal extracted via output waveguide 8. The tuning plunger 18 is axially movable by means of a spider assembly 19 contained within the tuner housing 5. The spider includes a plate like body 21 and dependent legs 22 passing through axial bores 23 in the upper pole piece 1 3. The legs 22 are connected at their inner ends to the backside of the tuning plunger 18.

A rod 24 is connected to the body plate 21 of the spider 19 and extends away from the anode circuit 11 in the axial direction. The upper end of the rod 24 is externally threaded to mate with the internal threads of a nut 25. The upper end of the nut 25 is connected to a ball and socket joint 26 which in turn is connected to a yoke member 27. The yoke member 27 contains a ball bearing assembly 2 8 concentrically mounted in bearing engagement on an eccentric drive shaft 29 which passes trans versely of the direction that the tuner actuating mechanism passes outwardly away from the anode circuit 11. The eccentric drive shaft 29 is merely an eccentric portion of the drive shaft of the motor 6 located between two centric portions of the drive shaft which ride in centric bearing assemblies not shown, fixedly mounted in the tuner housing assembly '5.

Thus rotation of the drive shaft 29 via motor 6 at a suitably high speed as, for example, 12,000 r.p.m., causes the yoke member 27 which rides on the eccentric portion of the shaft to oscillate in the axial direction at 12,000 oscillation per minute. The eccentric portion of the drive shaft is off center of the centric portion of the drive shaft by only about 0.0012" thus causing the tuner actuating mechanism with the dependent tuning plunger 18 to oscillate plus and minus 0.0012" about the mean axial position of the tuning plunger 18. This oscillatory motion of the tuning plunger 18 produces a dithering (frequency modulation) of the output frequency of the magnetron tube 1 about the carrier frequency of the output signal as determined by the mean position of the tuning plunger 18.

The mean axial position of the tuning plunger 18in the cavity 16, and thus the carrier frequency of the output signal of the tube 1 is changed by rotation of nut 25. The nut 25 cannot travel axially of the tuner actuating mechanism due to the axial restraining action of the ball and socket joint 26. Thus, rotation of the nut 25 causes the rod 24 to travel in or out of the nut 25 depending upon the sense of rotation of the nut, thereby changing the length of the tuner actuating mechanism and changing the mean position of the tuning plunger 18 within the cavity 16. This of course changes the carrier frequency of the frequency modulated output signal.

The nut 25 is rotated from a concentric gear 31, while oscillating to and fro in the axial direction, by either one of two means. A first means includes an axially flexible spider 32 as shown in FIG. 3. The spider includes a thin sheet of spring steel as of 0.007 thick formed with an annular body portion 33 and three radially outwardly directed leg portions 34. The legs 34 are secured via screws 35 to a lower face of the rotatable gear 31 which gear is captured against axial movement by peripheral thrust bearings 36. Thus the spider 32 rotates with the gear 31. The central body portion 33 of the spider 32 is secured to the nut 25 via screws 37. The leg portions 34 of the spider accommodates the axial to and fro oscillation of the nut while transferring rotational forces from the gear 31 to the nut 25 for rotation thereof.

The second means for transferring rotational forces to the nut 25 is shown in FIG. 4 wherein a pair of round flats 38, provided on the nut, bears in sliding engagement with a similar mating pair of out of round flats 39 axially projecting from the inner diameter of the top of the gear 31. A Worm shaft 41 meshes with the teeth of the helical gear 31 for rotating same.

Suitable sliding bearings are coaxially disposed of the tuner actuating mechanism to assure proper axial alignment and to prevent side to side motion thereof. A first bronze bushing 42 surrounds the tuner actuating rod 24 above the tuning spider plate 2.1. The bushing 42 is held in position by being mounted in an axial bore in a transverse mounting plate 43 of the tuner housing structure 5. A second bushing 44, as of Teflon, surrounds the cylindrical outer portion of the nut 25 and is mounted within the central aperture of the rotatable gear 31. -An O-ring seal 40 is mounted in the wall of the tuner housing around the upper portion of the nut 25 which contains the ball and socket joint 26.

The gear 31 is made of a two piece construction. An upper inverted cup shaped member 45 includes the pheripheral teeth on the outside wall portion. This cup member is fixedly secured to a lower centrally apertured disk member 46 via screws 47. The lower disk member 46 is restrained against axial movement by the peripheral thrust bearing 36 which in turn is :held to the transverse mounting plate 43 via mounting ring 48.

In operation, the eccentric shaft 29 causes the tuning plunger 18 to oscillate to end from about the mean tuning position of the plunger '18 by 0.0012". The mean position of the tuning plunger is axially movable over a range of about 0.200" by rotation of nut 25 which causes the rod 24 to move in and out of the nut to produce the 0.200 total travel of the plunger 18.

A bellows 51 is vacuum sealed at its ends to the underside of the transverse mounting plate 43 and to the spider tuning plate 21 to maintain the 'vacuum integrity of the tube 1 While allowing translation of the tuning structure. A compression spring 52 is placed between the tuning spider plate 21 and the underside of the transverse mounting plate 43 to put the tuner actuating mechanism including the mated threads of the nut 25 and the ball and socket joint 26 under 15 pounds of tension to prevent backlash and slack in the mechanism as the tuner must be non microphonic under severe vibration environments as encountered in helicopter and other airborne radar applications.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A ditherable and tunable microwave tube apparatus including, means for producing a stream of electrons,

means forming a microwave circuit for supporting wave energy for electromagnetic interaction with the electron stream to produce a microwave output signal, means for tuning said microwave circuit over a predetermined band of frequencies to tune the output signal over a band of frequencies, said tuning means including, a movable member portion disposed adjacent said microwave circuit for displacing a variable volume of the space adjacent said circuit for tuning thereof, means forming a tuner actuating mechanism connected at one end to said movable tuner member portion and extending in a certain direction away from said circuit, means mechanically coupled to said actuating mechanism for mechanically oscillating said actuating mechanism and said movable tuner member iportion dependent therefrom and means provided in said tuner actuating mechanism intermediate said tuner member portion and the point of mechanical coupling to said oscillating means for changing the length of said actuating mechanism between said tuner member portion and said point of mechanical coupling to said oscillating means, whereby the means position of said tuning member portion about which position oscillation thereof is produced is changed for tuning of the frequency of the microwave output signal to a frequency about which the output signal is frequency modulated by said oscillating means, said means for changing the length of said tuner actuating mechanism including, a nut forming a first portion of the tuner actuating mechanism, a threaded rod mating with the threads of said nut and forming a second portion of said tuner actuating mechanism, and means for producing rotation of one of said first and second portions of said mechanism and restraining the other portion from rotation, whereby the length of said actuating mechanism is changed.

2. The apparatus of claim 1 wherein said mechanical oscillating means includes, an eccentrically rotatable shaft with its axis of rotation transversely directed to the direction said actuating mechanism extends away from said circuit means, a yoke member concentrically mounted in bearing engagement with and on said eccentrically rotatable shaft whereby eccentric rotation of said shaft is transferred into oscillatory translation of said yoke member, and wherein said yoke member is mechanically coupled to said tuner actuating mechanism whereby the oscillator translation of said yoke member is transmitted to said tuner actuating mechanism to produce rectilinear oscillatory translation of said actuating mechanism with its dependent tuner portion along the direction which said mechanism extends away from said microwave circuit.

3. The apparatus of claim 2 including, means forming a ball and socket joint mechanically interconnecting said tuner actuating mechanism with said yoke member, whereby side to side whipping motio nof said yoke member is not transmitted to said tuner actuating mechamsm.

4. The apparatus of claim 3 wherein said first rotatable nut portion of said tuner actuating mechanism is connected between said ball and socket joint and said second rotationally restrained portion of said tuner actuating mechanism.

5. The apparatus of claim 4 including, an axially restrained rotatable gear concentrically mounted of said first rotatable nut, portion of said tuner actuating means, and means for transmitting rotation of said gear into rotation of said nut portion of said tuner actuating mechanism.

6. The apparatus of claim 5 wherein said means for transmitting rotation of said gear into rotation of said nut includes an axially flexible spider means interconnecting said gear and said nut.

7. The apparatus of claim 5 wherein said means for transmitting rotation of said gear into rotation of said nut includes means forming an out of round axially slidable bearing engagement between said nut and said gear.

8. The apparatus of claim 5 including, means providing a spring bias for putting said threadably mated first and second portions of said tuner actuating mechanism and said ball and socket joint in tension to prevent backlash and slack in the composite tuner actuating mechanism.

References Cited UNITED STATES PATENTS 2,512,901 6/1950 Litton 315-3961 2,589,885 3/1952 Sonkin 315--39.59 3,032,681 5/1962 Scanzani 315-39.61 3,157,818 11/1964 Olson 315-39.55 X

HERMAN K. SAALBACH, Primary Examiner.

S. CHATMON, JR., Assistant Examiner.

US. (:1. X.R. 

